Method of and apparatus for coating metal



April 30, 1929. 5M|TH 1,710,747

METHOD OF AND APPARATUS FOR COATING METAL Filed Dec. '7, 1925 INVENIOR F ATTORNEY the coatin The main object of the invention involves Patented Apr. 30, 1929.

' UNITED STATES PATENT OFFICE.

FRANKLIN SMITH, OF BRODKLYN, NEW YORK, ASSIGNOR T0 AMERICAN MAGNINE G; FOUNDRY COMPANY, A CORPORATION OF NEW JERSEY.

METHOD OF AND. APPARATUS FOR COATING METAL.

, Application filed December 7, 1925. serial 1%. 73,877.

This invention involves a method of, and an apparatus for, coating metal with anoncorrosive metal, relating more particularly to of ferric wire with lead.

the utilization of condensation of hot metallic vapor on relatively cold metal, and/or the utilization of'glow discharge to effect a bombardment of the metal or wire with 10 myriads of minute particles of lead or other protective metal. nother object of the invention is the production of a method of, and an apparatus for, coating metal by the use of these forces, in order that the coating 1 may be effected at a high rate of speed which has been heretofore unattainable, and at a greatly reduced cost of production. With these and other objects not specifically mentioned in view, the invention consists in certam acts and series of acts, and in certain apparatus, constructions, and combinations, which will be hereinafter fully described and a then specifically set forth in the claims hereunto appended.

The figure in the drawing illustrates in section an apparatus constructed in accordance with the invention, and by means of which the method may be carried into eifect. The invention involves as essential elements a method of coating metal and an apparatus for carrying that method into effect. The method consists in the condensation of metallic vapor upon the metal object to be coated. This condensation may be effected by temperature difference, or, preferably,

by electricdeposition of the vapor particles by means of the glow discharge. By the preferred method, the vapor particles in the neighborhood of the molten metal become ionized chiefly by glow dischar 'e. The ions combine with or condense upon the vapor particles, dragging these with them to the object to be coated, which is of opposite polarity.

The velocity of the vapor particles is proportional to their charge and to the voltage sure is maintained at a pressure less than atmospheric. I I

In the best practice of the method, therefore, the self-depositive properties of the vapor are thereby so augmented that the metal may be properly coated by passing it through the vapor as rapidly as it is practicable to handle it. The best practice of the method further contemplates sandblasting, or otherwise cleaning, the metal immediately before it is immersed in the metallic va or, or passed therethrough. When sandlasting is employed, the air used tends to prevent ingress of air to the coating chamber which confines the atmosphere embracing metallic vapor at subnormal pressure, by blowing the sand outwardly through the metal inlet of the chamber. And, similarly, when the coating is to be chilled, the air used tends to prevent ingress of air to the coating chamber, by blowmg outwardly through the metal outlet of the chamber.

The method branch or essential element of the invention may be varied within the scope of the method clalms; and the specific apparatus created for carrying the method into effect, and used to illustrate the invention, is but one of numerous possible concrete embodiments of the same. The invention, therefore, is not to be restricted to the precise details of the method and apparatus branches or essential elements of the invention shown and described.

The apparatus shown was especially created for coating ferric wire with lead; and it is provided with a coating chamber 1 hav= ing at its bottom an inlet 2 through which the wire to be coated is introduced into the chamber 1, and having at its top an outlet 3 through which the coated wire passes out of the apparatus. The coating chamber 1 is mainly in the form of a steel cylinder having a removable cover 4 at its top. Extending upwardly from the centre of this cover is a tube 5 which terminates at the outlet 3 before referred to. Extending downwardly from the centre of the bottom of the cylinder is an expansion tube 6 which terminates at the inlet 2 before referred to. In the operation of the apparatus, the wire to be coated passes upwardly through the inlet 2, the expansion tube 6, the centre of the cylv lead or other metallic vapor of a self-dc positive nature. This vapor is produced by the following instrumentalities: Suspended from the cover 4, by means of lead-ins 7, 8, is a meltin pot 9 of annular form, the wire to be coated passing up through an aperture 10 at its centre. The pot 9 rests on a centrally-apertured disc 11 through which the lead-ins 7 and 8 pass. The pot 9 is surrounded by a heating coil 12 which is ineluded in a low voltage circuit ((3 volts) of high amperage, said circuit also including the lead-ins 7 and 8. The coil 12 beats the lead or other metal in the pot 9 to maintain the desired vapor pressure within the coating chamber 1. Surrounding the coil 12 is a heat shield 13 ot'xgraphite for preventing overheating of the coating chamber walls opposite the pot 9. The lead-ins 7 and 8 are supported by insulators 14, let, screwed into the cover 4 before referred to. These insulators may be made of the well-known fused silica. Each is surrounded by a metallic tube 15 the purpose ofwhich is the prevention of condensation of metallic vapor on the insulators which, if permitted, would short-circuit the apparatus and render it useless. The condensation of the metallic vapor is prevented by the dielectric fields between the lead-ins 7 and 8 and the tubes 15. One side of the high voltage circuit is grounded on the vacuum chamber 23 as indicated on the drawing; the insulated side enters the coating chamber 1 through the lead-in 7 which is insulated from ground by the insulator 14. Connection is made to the metal in the pot 9 through the heating coil 12, the lead-in 8 and pipe 19. The low voltage circuit, which obviously is insulated from? The hollow part of the lead-in 8 terminates at its lower end at a T 18 with which is connected a bent pipe 19 leading to the interior of the pot 9. When the pot 9 needs replenishing, molten metal is forced from the receptacle 17 through the pipe 16, T 18,

and pipe 19, to the pot 9.

As has been indicated in the foregoing, the metallic vapor pressure in. the coating chamber 1 is maintained at a pressure less than atmospheric. -Means are provided therefor which include a suction duct 20 leading from the tube 5, before referred to, towards a suitable vacuum pump of wellknown construction and operation and therefore not shown in the drawing. Air is exhausted from the vapor chamber 1 by this means until a pressure of ap roximately 10 inches of mercury is reache or, in other words, until the pressure is approximately 20 inches below normal atmospheric pressure at sea level. And there it is maintained as constantly as possible.

In order to increase the etliciency of the apparatus, means are provided to prevent water from entering the vacuum chamber 26 or the pump. \Vith this end in view, there is provided a duct 21 connected with the expansion tube 6 at one end and to the dchydrating chamber 22 at the other end. A similar dehydrating chamber 28 is connected to the vacuum chamber 26 by means of a duct 27. Each of these dehydrating chambers contain a suitable deliqucscent salt, for example phosphorus pentoxide, indicated on the drawing as 23. The outlets of these dehydrating chambers are indicated on the drawing by arrows and are connected to suitable pumps of well known construction and operation and not shown on the drawing.

For the purpose of cleaning the wire immediately before it enters the coating chamber 1, there is provided means for sandblasting it at the inlet 2. This sand-blasting means includes a suitable blower of wellknown construction and operation and therefore not shown, and a sand-blast pipe 24 opening into the tube 6 near the inlet 2 in such manner as to blow outwardly through the inlet 2. thus effectually cleaning the wire immediately before it enters the coating chamber 1 and insuring a clean surface for the reception of the lead or other metal coating. Moreover, this outgoing blast of air and sand etfectually prevents ingress of air through the inlet 2, thus preventing disturbance of the partial vacuum existing in the chamber 1.

For the purpose of cooling or chilling the coating on the wire immediately after it has been applied, provision is made for a cooling blast of air blowing outwardly through the oulet 3 before referred to. This includes a bent pipe 25 so associated with the outlet 3 as to direct a blast of cool air out through said outlet with the wire, thereby cooling or chilling the coating on the latter. The air blast flowing through the pipe 25 is derived from a suitable blower of well-known construction and operation and therefore not shown. It prevents ingress of air, thus avoiding disturbance of the partial vacuum existing in the chamber 1.

Naturally, the coating chamber 1 must be very hot, and in order to provide heat insulation for the same, the said coating chamber is surrounded by a vacuum chamber 26 wherein a vacuum as nearly perfect as 2 possible is desirable. The dehydrating For the purpose of cooling the tops of the coating chamber 1 and vacuum chamber 26, a series of water pipes 29 lie coiled about the uppersurface of the coating chamber cover 4, and a similar series of water pipes 30 he coiled about the upper surface of the vacuum chamber 26.

\Vhen coating by condensation alone, atmospheric pressure may be used, though low pressure results in more rapid condensation. The lower the pressure, the lower the temperature at which the method may be worked. But when coating electrically, either alone or in conjunction with condensation, low pressure is essential, and the relai tive high voltage must be unidirectional. There is a. choice of polarity, however, as abetter and more rapid deposit is obtained by cathodic bombardment; that is, when the metal to be coated is positive.

The operation of the apparatus is as follows: Assuming that the vacuum pumps have been working long enough to produce a partial vacuum in the coating chamber 1, and a suflicientl .low pressure in the vacuum chamber 26, an that the low voltage circuit including the heating coil 12 has been in operation long enough to heat the lead or other metal in the pot 9 to the desired vapor pressure wire to be coated may then be led upwardly'through the apparatus, as by wire 'already coated and married to its end for thispurpose. The incoming wire is thoroughly cleaned by the sand blast at the inlet, and when it reaches a point just above the melting pot 9, the difference of temperatures of the hot vapor and of the cold wire results in condensation of vapor on the surface of the wire. By the preferred method, however, the metallic vapor is condensed on the metal to be coated by electrical deposition as has been indicated in the foregoing.

A unidirectional current of about 2,000

- "olts is employed, the energy of which is limited to prevent transition from glow to are discharge. There is a choice of polarity as a better and more rapid deposit is obtained by cathodic bombardment; that is, when the metal to be coated is positive. As the wire to be coated passes through the coating chamber, it will be bombarded by myriads of metallic vapor particles which raipdly cons dense upon the wire and form a relatively thick and tenacious coating. The wire should be passed through the coating chamber as rapidly as it is mechanically practicable. As the coated wire emerges from the oulet 3, the coating is chilled by the air blast hereinbefore described. Once started, the operation is continuous, so long as the supply of metal in the pot is maintained.

Stuffing boxes, of well-known construction and operation and therefore not shown, may

be used instead of the outgoing blasts at the inlet 2 and outlet 3, if'desired.

Also, the tubes at the inlet 2 and outlet 3 may be approximately 20 feet long, in which case. no stufling boxes, and nooutwardlydirected air-blasts, will be required merely to maintain the low pressure in the coating chamber, for the reason that such great lengths relative to the small diameters of said inlet and outlet enables the pumps to maintain the low pressure in the coating chamber. Also, a smoothing die for the coated wire, of well-known construction and operation and therefore not shown, may be used at the outlet 3, if desired.

What is claimed is:

1. The method of metallically coating metal, which consists in thermally vaporizing the coating metal, then ionizing the metallic vapor, and electrically depositing and condensing the ionized vapor on the metal to be coated.

2. The method of metallically coating metal, which consists in thermally vaporizing the coating metal at sub-atmospheric pressure, ionizing the metallic vapor, and

,electrically depositing and condensing the ionized vapor on the metal to be coated.

' 3. Thewmethod of metallically coating metal, which consists in thermally vaporizing the coating metal, ionizing the metallic vapor,cleaning the metal to be coated, and electrically depositing and condensing the ionized vapor on the cleaned'metal.

4.. The method of metallically coating metal, which consists in thermally vaporizing the coating metal, ionizing the metallic vapor, passing the metal to be coated through the ionized vapor, and electrically depositing and condensing the ionized vapor on the passing metal.

5.v The method of coating ferric wire with lead, which consists in thermally vaporizing the lead, ionizin the lead vapor, and electrically depositing and condensing the ositin and condensin the ionized va or.

on the metal to be coated in said chamber, and means for cleaning the metal to be coated as it enters said chamber.

8.. An apparatus for coating metal, comprising a coating chamber, means for ther mally vaporizing coating metal in said chamber, meansdfor ionizing and electrically coated in said chamber.

10. An apparatus for coating metal, comprising a coating chamber having an inlet at its bottom and an outlet at its to 3 for the metal to be coated, means for thermally vaporizing coating metal in said chamber, and means for ionizing and electrically depositing and condensing the ionized vapor on metal passing through said inlet, said chamber, and said outlet.

11. An apparatus for coating metal, comprising a coating chamber having an inlet at its bottom and an outlet at its top for the metal to be'coated, means for thermally vaporizing coating metal in said chamber, means for ionizing and electrically depositing and condensing the ionized vapor on metal passing through said inlet, said chamber, and said outlet, and means for cleaning the metal to be coated as its passes through said inlet.

ber to establish pressure.

13. An prising a coating chamber, means for thermally vaporizing coating metal in said chamber, means for ionizing and electrically depositing and condensing the ionized va or on the metal to be coated in said cham )er, a suction duct leading from said chamber and dehydrating means associated with said duct.

14. An apparatus for coating metal, comprising a coating chamber, means for thermally vaporizing coating metal in said chamber, means for ionizing and electrically depositing and condensing the ionized vapor on the metal to be coated in said chamber, and a heat-insulating vacuum chamber surrounding said coatin chamber.

15. An apparatus For coating metal, comprising a coating chamber, means for thermally vaporizing coating metal in said chamber, means for ionizing and electrically depositing and condensing the ionized va or on the metal to be coated in said cham r, a vacuum chamber surrounding said coating chamber, and means for cooling the tops of both chambers.

16. An apparatus for coating metal, comprising a coating chamber having an inlet and an outlet each of which is of great length relative to its diameter, means for thermally vaporizing coating metal in said therein sub-atmospiheric 12. An apparatus for coating metal, comchamber, and means for ionizing and elecprising a coating chamber, means for thermally vaporizing coating metal. in said chamber, means for ionizing and electrically depositing and condensing the ionized vapor on the metal to be coated in said chamber, and a suction duct leading from said chamtrically depositing and condensing the ionized vapor on the metal to be coated in said chamber.

In testimony whereof, I have signed my name to this specification.

' FRANKLIN SMITH.

apparatus for coating metal, com- 

